Implantable medical devices are commonly used today to monitor and/or delivery therapy to a patient. In one example, many patients suffer from heart conditions that can result in a reduced ability of the heart to deliver sufficient amounts of blood to the patient's body. Such heart conditions may lead to slow, rapid, irregular, and/or inefficient heart contractions. To help alleviate some of these conditions, various medical devices (e.g., pacemakers, defibrillators, etc.) can be implanted in a patient's body. Such devices may monitor and in some cases provide electrical stimulation (e.g. pacing, defibrillation, etc.) to the heart to help the heart operate in a more normal, efficient and/or safe manner. In another example, neuro stimulators are often used to stimulate tissue of a patient to help alleviate pain and/or some other condition. In yet another example, an implantable medical device may simply be a monitor that monitors one or more physiological or other parameters of the patient, and to communicate the sensed parameters to another device such as another implanted medical device or an external programmer. To extend the effective lifetime of such implanted medical devices, there is a desire to conserve energy while still providing effective monitoring and/or delivery of therapy to the patient.